The present invention relates to a semiconductor laser device to be employed as a light source or the like of an optical pickup device for reading the data of, for example, CD-ROM (compact disc read only memory), DVD (digital versatile disc) or the like.
As a semiconductor laser device of this kind, there is the one shown in FIG. 8A (Japanese Patent Laid-Open Publication No. HEI 6-5990). This semiconductor laser device is the semiconductor laser device of a hologram laser system. As shown in the exploded perspective view of FIG. 8B, in this semiconductor laser device 100, a heat sink 102 is formed integrally with a base 101, and a semiconductor laser element 105 is mounted on a side surface of this heat sink 102 via a submount 104 for heat radiation. A light-receiving element 107 for signal detection use is mounted on the upper surface of the heat sink 102. A plurality of leads 108 are each fixed to the base 101 while being electrically insulated by hermetic seals 109. Pads (not shown) of the semiconductor laser element 105 and the light-receiving element 107 are connected by wire bonding (not shown) to inner leads 108a, which are the portions that belong to the leads 108 and protrude on the heat sink side of the base 101. Then, the heat sink 102, the semiconductor laser element 105, the light-receiving element 107 and the inner leads 108a, which are located on the base 101, are covered with a cap 110, and a hologram element 112 is fitted in an opening window 110a opened in a position that belongs to this cap 110 and is facing the semiconductor laser element 105.
FIG. 9A is a perspective view showing a prior art semiconductor laser device (Japanese Patent Laid-Open Publication No. HEI 6-5990), while FIG. 9B is an exploded perspective view of this semiconductor laser device. For the semiconductor laser device shown in FIGS. 9A and 9B, the portions that have the same functions as those of the semiconductor laser device shown in FIG. 8 are denoted by the same reference numerals, and no detailed description is provided for the portions. The semiconductor laser device 120 of FIGS. 9A and 9B differs from the semiconductor laser device 100 shown in FIGS. 8A and 8B only in that the base and the cap have different shapes. In this semiconductor laser device 120, the base 101 and the cap 110 are roughly elliptic in shape, where two opposed bow-shaped portions are removed from a circular shape, and this device has a width smaller than that of the semiconductor laser device 100 of FIG. 8. If this semiconductor laser device 120 is mounted with the widthwise direction thereof directed in the direction of thickness of the optical pickup device, then an optical pickup device that has a small thickness can be provided.
The semiconductor laser device shown in FIGS. 10A, 10B and 11 (refer to Japanese Patent Laid-Open Publication No. HEI 10-256649) differs from the semiconductor laser device 100 shown in FIGS. 8A and 8B in the structure of connecting wiring leads to the base. In FIGS. 10A and 10B, the portions that have the same functions as those of the semiconductor laser device of FIGS. 8A and 8B are denoted by the same reference numerals. As shown in FIG. 10B, this semiconductor laser device 125 has resin lead blocks 127 and 127 in which leads 108 are partially implanted. The resin lead blocks 127 and 127 are fixed by ultrasonic welding onto both sides of a base 101 on which the semiconductor laser element 105 and the light-receiving element 107 are mounted, forming a stem 128. Then, a cap 110 is fixed to this stem 128 so as to cover the semiconductor laser element 105, and a hologram element 112 is arranged in an opening window 110a provided on the upper surface of this cap 11, forming a semiconductor laser device 125.
This semiconductor laser device 125 is not required to insulate and fix a plurality of leads 108 to the base 101 each via the hermetic seals 109, dissimilarly to the semiconductor laser device 100 shown in FIGS. 8A and 8B, and therefore, the semiconductor laser device 125 can easily be assembled.
In each of the semiconductor laser devices 100, 120 and 125 shown in FIGS. 8A through 11, the cap 110 is provided with a flange portion 110b, and this flange portion 110b is resistance-welded to the end surface of the base 101, fixing the cap 110 to the base 101. The end surface of the base 101 to which the flange portion 101b is welded has a mounting reference surface 101a for mounting each of these semiconductor laser devices 100, 120 and 125 on the mounting portion of the optical pickup device in a portion other than the portion to which the flange portion 110b of the cap is welded.
FIG. 12 is a view showing an optical pickup device that employs the semiconductor laser device 120 shown in FIG. 9. It is to be noted that optical pickup devices that employ the semiconductor laser devices 110 and 125 shown in FIGS. 8 and 10 also have the same construction as that of the semiconductor laser device of FIG. 12.
In this optical pickup device, the semiconductor laser device 120 mounted on a mounting plate 132, a collimator lens 133, a mirror 134 and an object lens 136 mounted on an actuator (not shown) are assembled with an assembly plate 131. The semiconductor laser device 120 is mounted on the mounting plate 132 with the mounting reference surface 101a fit close to the mounting surface 132a of the mounting plate 132.
The above-mentioned optical pickup device operates as follows. Laser light emitted from the semiconductor laser device 120 is split into three beams by a diffraction grating provided in the hologram element 112, and these three beams are reflected on the mirror 134 and condensed onto an optical disk 138 by means of the object lens 136. Return light from the optical disk 138 passes through a path identical to that of the emitted beam and returns to the semiconductor laser device 120. The return light that has returned to the semiconductor laser device 120 is diffracted by the hologram pattern of the hologram element 112 and made incident on the light-receiving segment of the light-receiving element 107 of the semiconductor laser device 120.
When mounting the semiconductor laser device 120 on the mounting portion of the optical pickup device, the semiconductor laser device 120 is turned for adjusting the mounting position so that the three beams are appropriately condensed onto three pit lines 138a, i.e., the tracks on the optical disk 138, and thereafter fixed to this mounting plate 132.
However, the aforementioned prior art semiconductor laser devices 110, 120 and 125 have a problem that the devices tend to become loose when turned for adjusting the mounting position on the mounting plate 132. In more detail, when turning the semiconductor laser devices 110, 120 and 125, the mounting reference surface 101a is turned while being fit close to the mounting surface 132a of the mounting plate 132. However, the mounting reference surface 101a, which is the surface other than the welded portion of the end surface of the base 101 to which the flange portion 110b of the cap 110 is welded, has a very small area. Therefore, the area of contact of this reference surface 101a with the mounting surface 132a is very small. Therefore, when the semiconductor laser devices 110, 120 and 125 are turned, the direction of the semiconductor laser devices 110, 120 and 125 with respect to the mounting plate 132 becomes disadvantageously unstable and loose. As a result, there is the problem that the mounting accuracy of the semiconductor laser devices 110, 120 and 125 with respect to the optical pickup device is poor.
Accordingly, the object of the present invention is to provide a semiconductor laser device capable of being easily accurately mounted on the mounting portion of an optical pickup device.
In order to accomplish the above object, the present invention provides a semiconductor laser device comprising:
a semiconductor laser element;
a metallic base for mounting the semiconductor laser element and supporting wiring leads via insulators; and
a cap that is provided with an opening through which light from the semiconductor laser element is emitted, and the cap being fixed to the base by welding with the semiconductor laser element housed therein,
the cap having a skirt portion extended from part of its peripheral surface, and the skirt portion being fixed by welding to a side surface of the base other than its end surface that serves as a mounting reference surface for the semiconductor laser device.
According to the above construction, the skirt portion of the cap is fixed by welding to the surface that belongs to the base and is other than the end surface. Therefore, no flange of the cap is welded to the end surface that serves as the mounting reference surface of the base, dissimilarly to the conventional case. Therefore, the end surface of the base in the state in which the cap is fixed to the base has an area larger than that in the conventional case. That is, the area of the mounting reference surface for mounting this semiconductor laser device on the mounting portion of the optical pickup device is larger than in the conventional case. Therefore, an area of contact of the mounting reference surface with the surface of the portion for mounting this semiconductor laser device becomes larger than in the conventional case. As a result, even if the semiconductor laser device is turned in a state in which the mounting reference surface is made to abut against the surface of the mounting portion of the optical pickup device so as to adjust the mounting position of this semiconductor laser device, the semiconductor laser device does not become loose. With this arrangement, the accuracy in mounting the semiconductor laser device on the mounting portion is improved.
In an embodiment, a recess portion is formed on the side surface of the base, a projection is provided in the recess portion, the skirt portion is inserted into the recess portion, the inserted skirt portion is welded to the projection inside the recess portion, and the cap is fixed to the base.
According to the above embodiment, the skirt portion of the cap is inserted into the recess portion formed on the side surface of the base, and therefore, the portion of the cap does not project outwardly of the side surface of the base. Therefore, this semiconductor laser device becomes compact since there is no portion that is projecting outwardly of the base.
Moreover, the cap is fixed by inserting the skirt portion extended from part of the peripheral surface of the cap into the recess portion located on the side surface of the base. Therefore, by finely adjusting the length of insertion of the skirt portion into the recess portion, a distance between the base and the top surface of the cap is accurately determined. Therefore, if this semiconductor laser device is of a hologram laser system such that the hologram element is provided at the top surface of the cap, the distance between the semiconductor laser element of the base and the hologram element of the cap is accurately determined, and the mounting accuracy of the hologram element is improved. Moreover, since the recess portion to which the skirt portion of the cap is fixed is provided on the side surface of the base. Therefore, even if the thickness of welding for fixing this skirt portion to the recess portion is varied, the distance between the base and the top surface of the cap does not vary. Therefore, the distance between the semiconductor laser element and the hologram element is reliably determined with high accuracy.
Furthermore, the skirt is welded to the projection provided in the recess portion, and therefore, the welding portion is smaller than the portion to be welded to the entire surface of the recess portion. Therefore, the influence of welding distortion and the like on the base and the cap becomes reduced.
In an embodiment, a recess portion is formed on a side surface of the base, a projection being provided in the recess portion,
a resin lead block that is constructed by implanting wiring leads in an insulating resin and has a through hole,
the resin lead block is arranged in the recess portion of the base, with the projection inside the recess portion penetrating the through hole, and
the skirt portion of the cap is welded to an end surface of the projection.
According to the above embodiment, the skirt portion of the cap is welded to the projection of the base that penetrates the through hole of the resin lead block, fixing the base, the resin lead block and the cap. Therefore, it is not required to weld the flange portion of the cap to the end surface of the base, dissimilarly to the conventional case. Therefore, the area of the mounting reference surface formed on the end surface of the base becomes larger than in the conventional case, and the mounting position of the semiconductor laser device is stably adjusted without becoming loose when the semiconductor laser device is mounted on, for example, an optical pickup device. Furthermore, the plurality of wiring leads are attached to the base only by providing the resin lead block in the recess portion of the base. Therefore, a semiconductor laser device is easily manufactured at a lower cost than when a plurality of leads are individually attached to the base via insulators.
In an embodiment, the welding is resistance welding.
According to the above embodiment, the base and the cap are fixed easily and firmly by the resistance welding.
In an embodiment, the projection has a sharp end portion.
According to the above embodiment, the projection to which the skirt portion of the cap is welded has the sharp end portion. Therefore, the position in which the projection and the skirt portion come in contact with each other before being welded becomes approximately constant without variation. Therefore, the welding position becomes approximately constant. Moreover, the area of contact of the sharp end portion of the projection and the skirt portion also becomes approximately constant without variation. Therefore, for example, the density of a current that flows through the contact portion during the resistance welding also becomes approximately constant. Therefore, the area of the portion to be welded by the welding, the depth of melting of the material to be welded and so on become approximately constant, by which the skirt portion of the cap and the base are welded together with a specified quality free of variation. As a result, satisfactory welding, which ensures a specified strength, is stably obtained.
In an embodiment, the base has a length in a lengthwise direction and a length in a widthwise direction, the lengths being different from each other.
According to the above embodiment, by welding the skirt portion of the cap to the side surface of the base in the lengthwise direction whose length is different from that of widthwise direction, the welded portions of the base and the cap are allowed to be located in an appropriate position and have an appropriate area. Therefore, the base and the cap are easily welded together with an appropriate strength.
In an embodiment, the mounting reference surface for the semiconductor laser device is arranged at both ends in the lengthwise direction of the base.
According to the above embodiment, the mounting reference surface arranged at both ends in the lengthwise direction of the base, of which the distance between the reference surfaces located at both ends is greater than when the reference surface is arranged at both ends in the direction of the short side of the base, becomes stable with respect to a large moment force. Therefore, even if the semiconductor laser device is turned in order to adjust the mounting position of the semiconductor laser device in a state in which the reference surface abut against the mounting surface of the semiconductor laser device, the semiconductor laser device does not becomes loose. As a result, the mounting position of the semiconductor laser device is determined easily and reliably.
In an embodiment, two or more welded portions are provided in positions symmetrical with respect to an axis in the lengthwise direction of the base.
According to the above embodiment, two or more welded portions are provided in positions symmetrical with respect to the axis in the lengthwise direction of the base, and therefore, the cap is reliably fixed to the base with a specified strength.
The present invention also provides an optical pickup device provided with the semiconductor laser device of the present invention.
According to the above construction, the semiconductor laser device is easily mounted on the mounting portion of the optical pickup device with the specified mounting accuracy. Therefore, a thin type optical pickup device having a satisfactory performance is easily manufactured.